1. Field of the Invention
The present invention relates to a linear motor and a linear compressor using the same, and, more particularly, to a linear motor and a linear compressor using the same wherein a plurality of coil groups, provided in the linear motor, are connected in series or in parallel, and driving power is applied to part or all of the coil groups depending on the magnitude of load current applied to the linear motor, whereby the linear motor achieves an improved efficiency with a reduced size.
2. Description of the Related Art
Generally, a compressor is an apparatus to compress fluid, such as air or gaseous refrigerant. In particular, a linear compressor is designed to introduce, compress, and discharge gaseous refrigerant through a linear reciprocating movement of a piston in a cylinder, which is performed by a linear driving force of a linear motor.
Conventionally, the linear compressor comprises a hermetic container having a suction pipe that is connected to a certain location of the hermetic container to introduce refrigerant into the hermetic container, a cylinder mounted in the hermetic container and having a refrigerant compression chamber therein, a piston mounted to be linearly reciprocated in the cylinder and adapted to introduce the refrigerant into the compression chamber to thereby compress it therein, and a linear motor connected to an end of the piston to provide a driving force required to linearly reciprocate the piston.
The linear motor includes a stator having a coil assembly, and a mover having a magnet and a magnet frame to connect the magnet to the piston.
FIG. 1 is a circuit diagram of a conventional linear motor provided in a linear compressor.
As shown in FIG. 1, the conventional linear motor 1 includes a coil assembly 2 to produce a magnetic field when AC power is applied thereto, and a relay 5 to selectively transmit the AC power to the coil assembly 2.
The linear motor 1 is designed to vary the magnitude of a magnetic field depending on a load applied thereto, thereby achieving improved motor efficiency.
For this, the coil assembly 2, provided in the linear motor 1, consists of a main coil Cm and an auxiliary coil Cs. When the applied load is high, the linear motor 1 operates in a power mode wherein the relay 5 is connected to a connecting terminal 3 of the main coil Cm to increase the magnitude of electric current flowing into the main coil Cm. This increases the strength of the resulting magnetic field, achieving a lengthened stoke of a piston.
Conversely, when the applied load is low, the linear motor 1 operates in a save mode wherein the relay 5 is connected to a connecting terminal 4 of the main coil Cm and the auxiliary coil Cs to decrease the magnitude of electric current flowing into both the main coil Cm and the auxiliary coil Cs. This decreases the strength of the resulting magnetic field, achieving a shortened stoke of the piston.
FIG. 2 is a diagram illustrating the coil assembly of the conventional linear motor.
The coil assembly 2 includes a bobbin, and coils wound plural turns on the bobbin and adapted to produce a magnetic field when electric voltage is applied thereto.
As described above, the coils include the main coil Cm immediately disposed on the bobbin, and the auxiliary coil Cs disposed around the main coil Cm. The main coil Cm and the auxiliary coil Cs are connected in series.
However, the conventional linear motor configured and operated as stated above has a problem in that the size of the linear motor should be large to ensure successful operation of the liner motor in the low-load save mode.
Specifically, since the coils are conductive wires, such as copper wires, they basically have a predetermined magnitude of resistance. Generally, the resistance of a conductive wire is proportional to the length of the wire and inversely proportional to the cross sectional area of the wire.
Therefore, in the case of the save mode wherein driving power is applied to both the main coil Cm and the auxiliary coil Cs connected in series, the resistance of the wire increases due to the increased coil length, and consequently, the electricity consumption of the wire itself increases, resulting in deteriorated motor efficiency.
To solve the above problem, it may be regarded that a conducting wire having a large cross sectional area is used to reduce the resistance of the save mode to a level of the power mode. This solution is effective to improve the efficiency of the motor, but is still problematic because it unnecessarily increases the cross sectional area of the coil in the case of the low-load save mode, resulting in an increased motor size.
In particular, the linear motor is configured in such a fashion that the conductive wires (hereinafter, referred to as coil conductors) of the main and auxiliary coils are closely wound on the bobbin to be stacked one above another. However, if the cross sectional areas of the coil conductors increase, it is very difficult to wind the coils in the above manner.